Question: Solve for $x$ and $y$ using substitution. ${-x-y = 1}$ ${y = -3x+5}$
Since $y$ has already been solved for, substitute $-3x+5$ for $y$ in the first equation. ${-x - }{(-3x+5)}{= 1}$ Simplify and solve for $x$ $-x+3x - 5 = 1$ $2x-5 = 1$ $2x-5{+5} = 1{+5}$ $2x = 6$ $\dfrac{2x}{{2}} = \dfrac{6}{{2}}$ ${x = 3}$ Now that you know ${x = 3}$ , plug it back into $\thinspace {y = -3x+5}\thinspace$ to find $y$ ${y = -3}{(3)}{ + 5}$ $y = -9 + 5$ $y = -4$ You can also plug ${x = 3}$ into $\thinspace {-x-y = 1}\thinspace$ and get the same answer for $y$ : ${-}{(3)}{ - y = 1}$ ${y = -4}$